Table 1.

Vitamin K types, functions, and sources.

Type of vitamin K	Function in the human body	Sources of vitamin
Vitamin K1	(i) Participates in blood clotting. Serves as a cofactor for carboxylation of protein bound glutamate residues by converting them to carboxy glutamate (GLa). GLa containing proteins are found in Factors II, VII, IX, and X	(i) Green leafy vegetables and some plant oils
Vitamin K2, menaquinone-4 (MK-4)	(i) Osteocalcin (synthesized in bone) (ii) Matrix GLa protein (synthesized in cartilage and in blood vessel walls) It is involved in calcium transport, preventing calcium deposition in the lining of blood vessel walls, and helps improve bone density [1] (iii) Short chain form with shorter half-life	(i) Butter, eggs yolks, lard, and animal based foods (ii) Synthesis by bacteria in the intestinal tract (however, synthesized MK-4 is bound to the membranes of bacteria in the gut and very little is absorbed in humans) [5] (iii) Over-the-counter (OTC) supplements
Vitamin K2, menaquinone-7 (MK-7)	(i) As for MK-4 (ii) Long chain form with longer half-life	(i) Fermented foods, some cheese (ii) Extracted from Nattō (fermented soy) as an OTC supplement
Vitamin K3, menadione	(i) Has been banned by the FDA in the USA because of potential toxicity (hemolytic anemia) [6] (ii) Is presently being studied as a potential prostate/hepatocellular cancer therapy and potential treatment for skin toxicities secondary to kinase inhibitor therapy [7]	(i) ⁡Synthetic analogue of vitamin K considered a provitamin